Example of Semiconductor

Conductors?Most metals are good at conducting heat and electricity. Things like copper, aluminium, iron, gold...

Inuslators? Most (but not all) polymers (plastics) and ceramics are not very at conducting heat and electricity.
Things like polyethylene, polypropylene, PET, –and for ceramics– clay, porcelain, alumina...

Semiconductors? properties in between the two (but especially in terms of electrical conductivity (eg silicon, gallium arsenide)

Superconductors? Materials with zero resistance to electricity at low temperatures. Most metals superconduct at extremely low temps.

According to wikipedia, the highest temperature that this occurs at is for the material HgBa2Ca2Cu3O8 (Mercury Barium Calcium Copper Oxide) and it happens below -139°C. Trouble is, not very practical for making wires out of, is it? And it has Mercury in it, which is not eco friendly at all, because the element mercury is toxic.

According to the book I'm reading at the moment (cradle to cradle), just one gram of mercury will contaminate all the fish in a 20 acre lake. And it's quite dense so that is only 0.074 millilitres.

Perfect conductors? I'll admit that I have not actually heard of this before. Probably because I finished my undergrad degree in '99. It appears that perfect conductors have the same property as described above for superconductors (zero electrical resistivity), but without some other properties that superconductors exhibit (such as the Meissner effect, which is basically levitation in a magnetic field)

See here for a bit more info.

(looks like perfect conductors –also called ideal conductors– don't or can't actually exist in nature in the physical sense, they are just something physicists have invented up — usually to make theoretical calculations easier)